Cleaner for tin plated ferrous metal surfaces, comprising phosphate, silicate and borax

ABSTRACT

A composition and method for treating tin-plated ferrous metal surfaces to remove oils and other contaminants in the form of soil thereon, without etching the surface. Particularly, this invention relates to a composition and method for cleaning drawn and ironed tin-plated ferrous metal containers.

United States Patent 1 [111 3,888,783 Rodzewich June 10, 1975 [54]CLEANER FOR TIN PLATED FERROUS 3,645,905 2/1972 Rosenfeld et al. 252/135MET AL SURF ACES, COMPRISING 3,782,906 1/1974 Pierce 252/135 XPHOSPHATE, SILICATE AND BORAX Edward A. Rodzewich, Flourtown, Pa.

Assignee: Amchem Products, Inc., Ambler, Pa.

Filed: Oct. 10, 1973 Appl. No.2 405,187

Inventor:

US. Cl. 252/135; 117/49; 134/2;

252/DIG. 1 Int. Cl. Clld 3/06; Clld 3/08 Field of Search 252/135, DIG.1', 117/49 References Cited UNITED STATES PATENTS Schwedler 252/135Primary ExaminerLeland A. Sebastian Attorney, Agent, or FirmErnest G.Szoke; Howard S. Katzoff; Michael E. Zall 7 Claims, N0 Drawings CLEANERFOR TIN PLATED FERROUS METAL SURFACES, COMPRISING PHOSPHATE, SILICATEAND BORAX Containers used in the food stuff industry can be made oftin-plated ferrous metal. These containers are ordinarily formed througha process referred to as drawing and ironing, that is the tin-platedmetal sheeting is drawn and intentionally thinned to form a drawn sheetproviding uniform wall thickness and producing a thin walled, thickbottomed container. Due to the high cost of tin-plate, only a thin layerof tin-plating is employed.

During fabrication and forming of the tin-plated ferrous metalcontainer, lubricants are employed to facilitate the drawing and ironingoperation. The lubricants which are deposited on the metal surfaceusually consist of various types of mineral and vegetable oils and heavymetal soaps.

A serious problem with drawn and ironed tin-plated containers is thatthe drawing operation stretches the interior tin-plate surface therebyproducing pores which leave the underlying ferrous metal surfaceexposed. In order to clean the surface and remove the lubricantstherefrom, cleaners have been employed which not only remove thelubricant but etch the tinplated ferrous surface which aggravates theproblem of corrosion of the exposed steel surface through the poresleaving unsightly rust marks. Moreover, as the containers are processedduring manufacture, after the drawing and ironing step and the cleaningstep, conditions on the processing line, such as line stoppage, can leadto corrosion of the exposed ferrous surface, rendering the containersunacceptable for use. Any corrosion and blemishes formed on the surfacewill adversely affect the adhesion of any subsequent conversion coatingor sanitary lacquer coating which is applied thereafter.

A variety of cleaning compositions have been employed in the art totreat tin-plated ferrous metal surfaces in order to effect removal ofthe lubricants and forming oils on the surface. The use of cleaningcompositions which etch the surface at the same time removal of thelubricants is effected, are unsuitable due to the acceleration ofcorrosion of the surface. In addition, cleaning compositions known tothe art have not provided protection of the tin-plate surface subsequentto the cleaning step and prior to any further treatment such asconversion coating or sanitary lacquer coating.

This invention provides compositions for use in aqueous solutions toremove the lubricants employed to facilitate the drawing and ironingoperation, without etching the metal surface. The present invention alsoprevents corrosion of the exposed areas of ferrous metal for prolongedperiods of time prior to any subsequent treatment such as conversioncoating, or organic or sanitary lacquer finishing.

The principal object of the present invention is to providecompositions, solutions, and a process for cleaning tinplated ferrousmetal surfaces, in order to provide a clean surface suitable forsubsequent finishing treatments such as conversion coating and siccativefinish coating.

A particular object of this invention is to provide a cleaning solutionfor effectively removing lubricants from drawn and ironed tin-platedferrous metal containers without etching the surface.

A concomitant object of this invention is to provide novel cleaningcompositions and a method for their use for removing lubricants fromdrawn and ironed tinplated ferrous metal surfaces wherein the metalsurface is so conditioned that further surface treatment can be easilyperformed.

1 have discovered that a cleaning composition consisting ofmetasilicate, condensed phosphate, and sodium borate when added towater, will form an aqueous cleaning solution which effectively cleanstin-plated ferrous metal surfaces without etching the surface.

It should be understood that the term ferrous metal used herein includesiron, iron alloys, and a wide variety of steels. The term lubricants orlubricating material used herein means deposits formed on the metalsurface during the drawing and ironing step, which include various typesof mineral or vegetable oils and heavy metal soaps.

The term cleaning composition employed herein means the dry admixture ofmetasilicate, condensed phosphate, and Borax which, when added to water,is suitable for use in the process of the present invention. The termcleaning solution employed herein, means an aqueous solution formed fromthe addition of the dry cleaning composition to water, and comprisessilicate, condensed phosphate, and Borax, said solution suitable in thecleaning process of the present invention.

It will be appreciated that the metasilicates to be employed include thealkali metal metasilicates selected from the group consisting of sodiumand potassium. The addition of the alkali metal metasilicate to thecleaning solution not only increases the detergency of the solutionrendering it more effective in removing the lubricating materials, butthe silicate also provides added protection of the surface fromcorrosion prior to conversion coating. The silicate is also an excellentsaponifying agent for the lubricating oils and the residual loose dirton the surface.

Typical examples of the alkali metal metasilicates which can be used aresodium metasilicate, and potassium metasilicate. In the preferredpractice of the present invention, anhydrous sodium metasilicate shouldbe employed in the cleaning composition in order to prepare the aqueouscleaning solution. The sodium metasilicate is easily dissolved in waterand it offers the properties of high alkalinity and good detergency.

The condensed phosphate is an alkali metal phosphate selected from thegroup consisting of tripolyphosphate and pyrophosphate. Typical examplesof the alkali metal condensed phosphates which can be employed in thecomposition are sodium tripolyphosphate and sodium pyrophosphate. In thepreferred practice, sodium tripolyphosphate should be employed.

The borax in the cleaning composition can be in any suitable form, andpreferably should be present as sodium borate or sodium tetraboratepentahydrate.

The relative amounts of alkali silicate, condensed phosphate and boraxin the dry composition, expressed as a weight ratio, can be from about0.1 to about 0.5 parts by weight of alkali metasilicate for each part byweight of borax, and from about 0.1 to about 0.6 parts by weight ofcondensed phosphate for each part by weight of borax.

When the cleaning solution is prepared, the dry admixture or cleaningcomposition should be added to water in sufficient amounts to produce acleaning solution consisting of from about 0.75 grams/liter to about 3.0grams/liter of alkali metal metasilicate, from about 0.75 grams/liter toabout 7.5 grams/liter of alkali metal condensed phosphate, and fromabout 3 grams/liter to about grams/liter of borax. It should beunderstood that in the preferred embodiment of the present invention, asspecified hereinabove, the silicate portion of the cleaning compositionis comprised of sodium metasilicate and the condensed phosphate portionof the cleaning composition is comprised of sodium tripolyphosphate.Pyrophosphate can be substituted for the tripolyphosphate therebyproducing a substantially equivalent cleaning composition and cleaningsolution, in which case the concentrations of this material present inthe cleaning solution should correspond to that specified hereinabovewhen sodium tripolyphosphate is employed. The foregoing concentrationparameters are calculated on the basis of the sodium form ofmetasilicate and the sodium form of tripolyphosphate. As has been statedhereinabove, in the preferred embodiment of this invention the sodiumsalts are selected for use, but other alkali salts such as potassiumsalts can be substituted.

Surfactants and foaming agents are desirably included in the cleaningcomposition. Such materials enhance the cleaner performance but are notthe essence of the invention since they are used to perform functionsessentially similar to the function they perform in prior art solutions.Typical examples of surfactants and wetting agents which can be employedin the cleaning composition are ethoxylated straight chained alcoholsand octyl or nonyl phenoxy polyethoxyethanol. Preferably, non-ionicsurface active agents should be employed in the cleaning solution.

Typical examples of cleaning compositions suitable for dilution withwater to make cleaning solutions of optimum quality having constituentconcentrations and operating parameters in the ranges set forth herein,are

as follows:

FORMULA I by weight Sodium tripolyphosphate (anhydrous) 25 Sodiummetasilicate (anhydrous) 10 Sodium tetraborate pentahydrate 53 Nonionicsurfactants (NEODOL 25-9 and MAKON NF-lZ) l2 FORMULA II by weight Sodiumtripolyphosphate (anhydrous) Sodium metasilicate (anhydrous l5 boraxpentahydrate 53 nonionic surfactants (NEODOL -9 and MAKON NF-l2) l2FORMULA III by weight Sodium tripolyphosphate (anhydrous) 20 Sodiummetasilicate (anhydrous) 20 borax pentahydrate 48 nonionic surfactants(NEODOL 25-9 and MAKON NF-l2) l2 FORMULA lV by weight Tetrasodiumpyrophosphate 25 Sodium metasilicate l0 borax pentahydrate 53 nonionicsurfactants (NEODOL 25-9 and MAKON NF-l2) l2 FORMULA V by weight Sodiumtripolyphosphate (anhydrous) 26 Sodium metasilicate (anhydrous) 20 boraxpentahydrate 48 nonionic surfactants (NEODOL 25-9 and MAKON NF-l2) O6FORMULA VI by weight Sodium Tripolyphosphate 10 Sodium metasilicate 20borax pentahydrate 58 nonionic surfactants l2 The cleaning solution canbe applied to the substrate utilizing any contacting technique known tothe art. Preferably application will be effected by conventional sprayor immersion methods. The time of treatment of the tin-plated ferrousmetal surface with the cleaning solution need only be long enough toinsure complete wetting of the surface and can be as long as 20 minutes.Preferably, the surface should be treated for a time from about 15seconds to about 1 minute. A surprising aspect of present invention isthat the cleaning solution can be contacted with the tin-plated ferrousmetal surface for a period as long as 20 minutes without causing anyetching of the surface with a resulting loss in luster and staining ofthe surface. This is an important advantage especially on commercialprocessing lines, where line stoppage or breakdown readily occursthereby causing the cleaning solution to spray the tin-plated ferrousmetal containers for long periods of time. The present invention permitslong spray times without attack of the metal surface, wherein surfaceattack is prevented without the use of chromates.

The cleaning solution can be operated at temperatures as high as 190F.It is preferred that the cleaning process be operated at temperaturesfrom about to about F.

The cleaning solution is highly alkaline having a pH above about 9.0.The pH of the cleaning solution should be maintained at a level withinthe range of from about 9.0 to about 10.5.

During the cleaning operation, depletion of the constituents in thecleaning solution will occur due to factors such as drag-out and theaction of the constituents on the lubricating oils and loose dirt. Forexample, the silicate will be expended during its saponifying anddetergent action. Simple titration methods can be employed in order todetermine the concentrations of the condensed phosphate and silicate insolution. For example, the cleaning bath is maintained within itsprescribed operating parameters with suitable additions of theconstituents therein by separate additions of each constituent, whennecessary, or by addition of a replenishing composition having theconstituents in the same proportions in which they exist in themake-upcleaning composition.

The cleaning process can be accomplished by treating the tin-platedferrous metal surface after the drawing and ironing step. Generally, itis not necessary that the surface undergo any preliminary treatmentprior to contact with the cleaning solution. The cleaning process isaccomplished directly after the forming operating or a short period oftime thereafter.

Following the application of the cleaning solution, the surface iscompletely water-break-free. A waterbreak-free surface is completelyfree of lubricants, soil, and other contaminantsand will maintain 'acontinuous film of water.

Subsequent to the cleaning procedure, the metal surface is usuallyrinsed with water. The water rinse is necessary to remove any remainingresidues which may.

have remained after the cleaning step.

Subsequent to the cleaning process, the metal surface can be contactedwith a coating solution to provide a corrosion resistant coating whichalso enhances the adhesion of a later applied organic, sanitary lacquer,siccative finish or the like.

It has been discovered that when a coating solution comprising a primaryand/or secondary phosphate, a hydroxylamine salt, and a fluoride salt isapplied to a drawn and ironed tin-plated ferrous metal container,following the cleaning process of the present invention, excellentcorrosion resistant coatings are obtained. Optimum corrosion resistanceand sanitary lacquer adhesion has been obtained when a coating solutioncomprising monosodium and disodium monophosphate, hydroxylammonium acidsulfate, and ammonium bifluoride having the following formula is appliedto the surface:

by weight Monosodium Monophosphate .65 .85 Disodium Monophosphate .65.85 Hydroxylarnmonium Acid Sulfate .07 .05 Ammonium Bifluoride .03 .05Water 97.03 98.06

The surface which has been rendered clean and water break-free after thecleaning step of the present invention, when contacted with the coatingsolution described above maintains its original appearance, that is ahighly polished look having improved corrosion resistance and adhesionof a later applied sanitary lacquer or the like.

A particular advantage of the present invention is that after thecleaning step has been accomplished, the tin-plated ferrous metalsurface will not suffer corrosive attack when subjected to prolongedexposure to air prior to application of the conversion coating.

The examples presented below are illustrative of this invention and arenot considered as limiting for other materials and operating conditionsfalling within the scope of this invention that might be substituted.

EXAMPLE 1 Tin-plated drawn and ironed steel containers were employed inthis procedure. A cleaning solution was prepared by adding grams of thecomposition of Formula I to 1 liter of water, with stirring such thatcomplete dissolution of the constituents was achieved. The pH of thesolution was measured at 9.5.

The test containers were sprayed with the solution for a period of 20minutes at 40 psi and at a temperature of about F. After treatment, thecontainers were rinsed with water and visually observed for etching,gloss, and detinning. The test containers had a bright, rust freeappearance with no tin loss or etching.

EXAMPLE 2 Tin-plated steel containers were employed in this procedure.Test solutions were prepared employing the compositions of Formulas I,ll, Ill, and IV. Each of the aqueous cleaning solutions was prepared byadding 15 grams of each of Formulas I, II, III, and IV to 1 liter ofwater. The pH of the resulting cleaning solutions were measured and arelisted in Table 2 below. Sets of test containers were sprayed at 40 psiwith the respective solutions for a period of 1 minute. Other sets oftest containers were sprayed with each respective solution of 40 psi fora period of 20 minutes. The temperature of the cleaning solutions wasmaintained at F.

After treatment the containers were visually observed for etching andfor appearance. The results are bright, rust-free surface Tin-platedsteel panels were cleaned with a solution prepared as in Example 1 byspraying the containers at 5 psi for 45 seconds at 150F. After cleaninghad been accomplished the containers were then sprayed with an aqueouscoating solution having the following constituents:

by weight Mono-sodium monophosphate .53 Disodium monophosphate .47Hydroxylammonium acid sulfate .12 Ammonium bifluoride .06 Water 98.82

The pH of the above solution was measured at 5.2. The solution wasapplied to the containers at a pressure of about 5 psi and at atemperature of about 90F. for 45 seconds. The containers were thenrinsed with water, followed by a dionized water rinse and dried atambient temperature. The containers were visually observed and retaineda rust-free and bright appearance after treatment.

An acrylic white base paint (Celanese 641481) was thereafter applied tothe test specimens. The .test specimens were then subjected to animmersion test. In this procedure, the painted test specimens areimmersed in boiling deionized water for 30 minutes. The specimens areremoved from the boiling water and rinsed, then blotted dry. Portions ofeach of the test specimens are immediately scribed with a cross-hatchtool having eleven cutting blades spaced 1 millimeter apart. Using thecross-hatch tool, 100 squares measuring 1 millimeter by 1 millimeter arescribed on the painted surface. This is accomplished by drawingthescribing device across the area to be tested and then repeating theprocedure by drawing the device across the same area but at a 90 angleto the first scribing. The cross-hatched area is subjected to a tapeadhesion test wherein tape is applied firmly to the surface of the testspecimen over the entire cross-hatched area so that no air bubbles orwrinkles are present between the tape and the surface. The tape isallowed to set for one minute and is then drawn back against itself witha rapid pulling motion in a manner such that the tape is pulled from thesurface of the specimen.

The test specimens showed excellent paint adhesion with little or nopaint loss.

I claim:

1. A cleaning composition which when added to water forms an aqueoussolution for cleaning tin-plated ferrous metal surfaces, consistingessentially of an alkali metal metasilicate, a condensed phosphateselected from the group consisting of tripolyphosphate andpyrophosphate, and borax, wherein for each part by weight of borax insaid composition there is from about 0.1 to about 0.5 parts by weight ofalkali metal metasilicate and from about 0.1 part to about .6 parts byweight of condensed phosphate.

2. The composition of claim 1 further comprising a nonionic surfactant.

3. The composition of claim 2 wherein the alkali metal metasilicate issodium metasilicate present in a concentration of 10 percent by weight,wherein the condensed phosphate is sodium tripolyphosphate .present in aconcentration of 25 percent by weight, wherein the borax is present in aconcentration of 53 percent by weight, and wherein the nonionicsurfactant is present in a concentration of 12 percent by weight.

4. An aqueous cleaning solution for treating tinplated ferrous metalsurfaces consisting essentially of an alkali metal metasilicate in anamount of from about 0.75 grams/liter to about 3.0 grams/liter, acondensed phosphate selected from the group consisting of alkali metaltripolyphosphate and alkali metal pyrophosphate in an amount of fromabout 0.75 grams/liter, to about 7.5 grams/liter and sodium borate in anamount of from about 3 grams/liter to about 15 grams/liter.

5. A solution as in claim 4 having a pH of from about 9 to about 10.5.

6. A solution as in claim 4 further comprising a nonionic surfactant.

7. A solution according to claim 4 wherein the alkali metasilicate issodium metasilicate and the alkali metal condensed phosphate is sodiumtripolyphosphate.

1. A CLEANING COMPOSITION WHICH WHEN ADDED TO WATER FORMS AN AQUEOUSSOLUTION FOR CLEANING TIN-PLATED FERROUS METAL SURFACES, CONSISTINGESSENTIALLY OF AN ALKALI METAL METASILICATE, A CONDENSED PHOSPHATESELECTED FROM THE GROUP CONSISTING OF TRIPOLYPHIOSPHATE ANDPYROPHOSPHATE, AND BORAX WHEREIN FOR EACH PART BY WEIGHT OF BORAX INSAID COMPOSITION THERE IS FROM ABOUT 0.1 TO ABOUT 0.5 PARTS BY WEIGHT OFALKALI METAL METASILICATE AND FROM ABOUT 0.1 PART TO ABOUT .6 PARTS BYWEIGHT OF CONDENSED PHOSPHATE.
 2. The composition of claim 1 furthercomprising a nonionic surfactant.
 3. The composition of claim 2 whereinthe alkali metal metasilicate is sodium metasilicate present in aconcentration of 10 percent by weight, wherein the condensed phosphateis sodium tripolyphosphate present in a concentration of 25 percent byweight, wherein the borax is present in a concentration of 53 percent byweight, and wherein the nonionic surfactant is present in aconcentration of 12 percent by weight.
 4. An aqueous cleaning solutionfor treating tin-plated ferrous metal surfaces consisting essentially ofan alkali metal metasilicate in an amount of from about 0.75 grams/literto about 3.0 grams/liter, a condensed phosphate selected from the groupconsisting of alkali metal tripolyphosphate and alkali metalpyrophosphate in an amount of from about 0.75 grams/liter, to about 7.5grams/liter and sodium borate in an amount of from about 3 grams/literto about 15 grams/liter.
 5. A solution as in claim 4 having a pH of fromabout 9 to about 10.5.
 6. A solution as in claim 4 further comprising anonionic surfactant.
 7. A solution according to claim 4 wherein thealkali metasilicate is sodium metasilicate and the alkali metalcondensed phosphate is sodium tripolyphosphate.